1. the Herbicide

SPRING 2003 VOLUME 5.1 C O O P E R A T I V E E X T E N S I O N U N I V E R S I T Y O F C A L I F O R N I A CCCCC OOOOO - ---- H HHHH OOOOO RRRRR TTTTT The Herbicide Contaminated Compost Issue INSIDE THIS ISSUE Dennis Pittenger Area Environmental Horticulturist, Central Coast & South Region 1. The Herbicide Con- taminated Compost Jim Downer Issue Environmental Horticulture Advisor, Ventura County University of California Cooperative Extension An overview of clopyralid contami- erbicide contaminated composts have Clopyralid Products and Use nated compost, the herbicide’s properties, suddenly come to the fore as another and recommendations Himportant environmental issue threat- Clopyralid is a pre- and post-emergent her- for the landscape ening California’s landscape and greenwaste bicide with activity against a narrow range industry are included. recycling industries. Starting in 2001, articles of certain annual and perennial broadleaf began appearing in some of the state’s ma- weeds. Products containing clopyralid have 2. Runoff Water Quality jor newspapers which focused the public’s been on the U.S. market for more than 17 Laws and Their attention on the issue and raised its level of years and have been registered in California Enforcement in importance. It is borne out of problems that since 1997. California began in Washington state where herbicide- contaminated composts were found to be Clopyralid is a constituent of products sold Strict federal and state causing injury to garden plants. under several trade names registered for a water quality regula- tions are reshaping the variety of uses including cropland, rangeland, way agricultural Clopyralid was confirmed as the culprit by the turfgrass, roadside right-of-way and other operations are con- manufacturer, DowAgrosciences (formerly non-crop applications. Confront is a ducted and the known as DowElanco). Clopyralid residue has turfgrass herbicide that also contains direction of research since purportedly been found in finished com- programs in California tryclopyr and is registered for use in commer- and throughout the posts in California, but so far no plant dam- cial turfgrass applications and golf. Lontrel United States. age from tainted compost has been reported is an herbicide containing only clopyralid that in this state. The problem occurred in spite is also registered for commercial turfgrass. of warning language on many product labels Stinger is a product registered for use in ag- 3. Kikuyugrass to avoid composting clopyralid-treated plant ricultural crops, and Transline is used for in- Kikuyugrass cannot be material. This sparked a storm of controversy dustrial and right of way weed control. controlled with a and concern in the green industry and the Trupower is formulated for use by Trugreen/ single treatment or public over the safety of composted Chemlawn in their commercial applications procedure. A combi- greenwastes here in California. The follow- to turfgrass. Millenium is formulated by nation of cultural ing discussion is intended to provide infor- Scotts as a fertilizer/herbicide granule for practices and herbicide applications are mation on clopyralid and the problems it use in golf and commercial turfgrass appli- most effective. causes in compost, the California situation, cations. Millenium Ultra, formulated by and suggest steps the landscape industry Riverdale Chemical Company, is a combina- can follow to minimize contamination of com- tion product (clopyralid, 2,4-D, and dicamba) post. registered for use on ornamental turf sites Spring 2003 Volume 5.1 CC OO -- HH OO RR TT 2 such as golf courses and lawns. No clopyralid products persist in the environment from a month to over a year. are available for use by homeowners in California. Its persistence is greatest in soils that are low in oxygen (compacted or water saturated most of the time) and low Clopyralid has excellent activity against certain difficult to in microorganism activity (cold, heavily graded or disturbed control leguminous weeds. In turfgrass it is particularly soils). It is degraded almost entirely by microbial action in effective in controlling clovers and dandelions. Use of soils or aquatic sediments, but not by sunlight or contact clopyralid enables applicators to attain control of certain with water. Microbial break down rates are highest in broadleaf weeds with fewer herbicide applications. How- warm, moist soils that are low in organic matter, and low- ever, a relatively limited amount of clopyralid is used in est in cold, dry, compacted or waterlogged soils. California on turfgrass due to its expense and narrow reg- istration of uses. The only identified clopyralid degradation product is car- bon dioxide. The inability of clopyralid to bind with soils Clopyralid Basics and Mode of Action and its persistence imply that it has the potential to con- taminate water resources and non-target plant species, Clopyralid is a plant growth regulator herbicide from the but no extensive offsite movement has been documented. picolinic acid group of compounds. In susceptible plants, Clopyralid is low in toxicity to aquatic animals and very low clopyralid disrupts auxin-regulated processes, including in toxicity to most animals, but it can cause severe eye cell respiration and growth, causing uncontrolled and dis- damage including permanent loss of vision in humans. organized plant growth that leads to plant death. Uptake of the herbicide is either through roots or leaves, and it is Toxicity Problems and Compost Contamination both phloem and xylem mobile. Translocation throughout the plant is rapid and the material accumulates in grow- Toxicity problems started in Spokane, Washington when ing points of the plant where it has its primary effect. symptoms were first noted on tomato plants. Clopyralid was found as a contaminant in greenwaste composts in- Clopyralid affects sensitive plants at a concentration as corporated in to the soil or applied around plants as mulch. low as 10 parts per billion, — a very low concentration. The problem was noted at about the time that curbside Typical clopyralid toxicity symptoms include curved and recycling of green wastes and the associated composting twisted stems and leaves, cupping and crinkling of leaves, programs began in that state. Since grass clippings are stem cracking, and hardened growth on stems and leaves. an important component in that state’s green wastes, they Complete browning and death can take a couple of weeks were soon identified as the source of the herbicide, and for seedlings or an entire season for susceptible peren- the origins of it were traced back to applications of Con- nial or woody plants. front to residential lawns. Clopyralid is more selective (kills a more limited range of There are a number of desirable crop and ornamental plants) than some other auxin-disrupting herbicides like plant species among the families which clopyralid might picloram, triclopyr, or 2,4-D. Like these herbicides, affect including tomato, pepper, eggplant, potato, beans, clopyralid has little effect on grasses and other monocots. peas, sunflower, chrysanthemum, daisy, petunia, acacia, Also, clopyralid does little harm to members of the mus- honey locust and other leguminous plants. Age of the tard family (Brassicaceae) and several other groups of plant and rate of herbicide application will greatly impact broad-leaved plants. The basis of its selectivity is not well the degree of injury that might occur. Plants are most understood. Clopyralid is primarily effective against four tolerant to clopyralid applications when they are estab- plant families: Asteraceae (sunflower family); Solanaceae lished and when there is some woody tissue around the (nightshade/tomato family); Fabaceae (legumes/peas/ stem or trunk. Thus, it is believed that woody plants are clover family); and the Polygonaceae (buckwheat/knot- less likely to be damaged from the presence of clopyralid- weed family). contaminated compost in the landscape. Clopyralid is water-soluble and does not bind strongly with The characteristics of clopyralid allow it to remain active soils or evaporate easily. The chemical breaks down com- and available for plant uptake for a long period, thereby paratively slowly in soil and persists in plant material, even reducing the amount of herbicide and number of applica- in non-susceptible and non-target species. Clopyralid may tions needed to achieve control of susceptible plants. Spring 2003 Volume 5.1 CC OO -- HH OO RR TT 3 Conversely, its characteristics cause a significant problem bedded on granules of 12-12-12 fertilizer. Sprayed plots when greenwaste from clopyralid-treated plants is received equivalent rates of fertilizer nutrients. Turf clip- composted. Clopyralid survives the composting process ping samples were collected in each mowing regime at 0, and very little of its residue is needed to cause toxic ef- 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 weeks after clopyralid fects on non-target plants that come in contact with fin- treatment. Regardless of formulation, the mowing treat- ished composts used as soil amendments or mulches. ment did not impact clopyralid concentration in clippings. By four and ten weeks after application, clopyralid con- Considerable study has been undertaken by the manu- centrations in clippings were 7% and 0.4% of their initial facturer to understand the persistence of clopyralid. concentrations in sprayed and granular formulation plots, Clopyralid persists to a variable degree in soil when ap- respectively. Concentrations still averaged 150 ppb in clip- plied to turfgrass or directly to soil as a pre-emergent treat- pings at ten weeks after application, which would be high ment, so it remains available for any plants present to enough in compost to cause injury to many plants. What take it up and translocate it. However, it was discovered is not known is what the final clopyralid concentration in that when grass clippings or other plant materials con- compost would be based on an initial concentration of taining clopyralid are composted, the herbicide becomes 150 ppb.

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